This invention relates to footwear, and is particularly suitable for athletic footwear.
Over the decades, a variety of shoe structures have been devised for cushioning the impact of heel strike. Many of these include the use of gaseous and/or liquid chambers in the shoe sole. Often these are complex and costly, even to the point of being totally impractical. Exemplary of these are:
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The prior concepts/structures for effecting cushinging typically extend over the forefoot and heel of the sole, either as one chamber extending the length of the sole, or a heel chamber and a forefoot chamber connected by passageways. The forefoot portion is normally provided to receive fluid from the heel zone and then force the fluid back to the heel zone by pressure of the forefoot during foot roll and toeoff, in preparation for the next heel strike. These structures with fluid action beneath the forefoot allow the foot to flex laterally during foot roll and toeoff, too often resulting in instability beneath the foot so as to allow excessive pronation and/or supination with consequent potential damage or injury, particularly to the ankles and knees. Moreover, such devices do not accommodate the different impact forces resulting from different speeds of an activity, e.g. running vs. jogging. Thus, while serving to lessen the problem of impact force, they introduce the problem of instability.
Recent commercial embodiments of shoes for cushioning impact include the use of a gel in the shoe soles by one manufacturer, and of a pressurized air bladder in the shoe soles by another manufacturer. Such devices do in fact effect certain impact cushioning as has been determined by testing. However, tests show that the impact absorption of such devices, though beneficial, still exhibits sharp peak impact loads considered undesirably high. Moreover, these materials, being encapsulated under pressure and confined to a finite space, are not considered effective in accommodating different impact forces from persons of different weight or running at different speeds.
Such structures act primarily like a spring such that, following the impact of the foot, the subsequent shock tends to comes back and go right back up the person's heel. Devices acting like a spring also tend to be non-accommodating to different impact loads and rates of impact. Thus, a shoe which nicely accommodates a slow gait with proper cushioning could bottom out at a faster gait, and a shoe accommodating a faster gait would tend to be too stiff at a slower gait.